Process for producing polyhexamethylene suberamide



United States Patent 3,549,516 PROCESS FOR PRODUCING POLYHEXAMETHYL- ENESUBERAMIDE David Kiriraldy, Ragian, England, assignor to ImperialChemical industries Limited, London, England, a corporation of GreatBritain No Drawing. Continuation of application Ser. No. 560,783, June27, 1966. This application Aug. 15, 1969, Ser. No. 850,677 Claimspriority, application Great Britain, June 28, 1965, 27,279/65 Int. Cl.C08g 20/20 US. Cl. 260-78 2 Claims ABSTRACT OF THE DISCLOSURE A processfor producing a high softening point polyhexamethylene suberamide (nylon6.8) and the composition produced which has a Vicat softening point ofat least 234 degrees centigrade. The composition is produced utilizing anovel source of very pure suberic acid. The nylon 6.8 produced isparticularly suitable for textile and tire cord usage because of greatlyimproved properties, particularly the ease of obtaining high relativeviscosities and the resulting high tenacity compared to previously knownnylon 6.8 materials.

This application is a continuation of Ser. No. 560,783, filed June 27,1966, now abandoned.

The present invention is concerned with improvements relating topolyarnides and has exclusive reference to polyhexamethylene suberamideand to the process for its manufacture and to filaments and fibresobtained therefrom.

Polyhexamethylene suberamide, hereinafter referred to as 6.8 nylon, isknown from the literature from which it is clear that it can be meltspun into filaments. However there is little published informationrelating to the properties of the polymer or the filaments obtainedtherefrom by melt spinning. Such published information as there issuggests, at least by implication, that the properties are inferior tothose of polyhexamethylene adipamide (66 nylon) polymer or filaments(see, for example, Journal of Polymer Science, 1947, vol. 2, No. 3, page306).

In the past experimental amounts of nylon 6.8 have been prepared by thecondensation of hexamethylene diamine with suberc acid usingconventional polymerisation techniques, the suberic acid used in suchpreparations having been obtained via the oxidation of castor oil. Theoptical melting point for polyhexamethylene suberamide so obtained beingquoted in the literature as 215 C. to 220 C. We have now made theunexpected discovery that if nylon 6.8 is prepared from hexamethyleneadipamide and suberic acid which has been obtained synthetically, e.g.via the dimersation of butadiene to cyclooctadiene then by oxidationinto suberic acid, the resultant polymerhas a Vicat softening point ofat least 234 C. that is 14 C. to 19 C. higher than the previously quotedoptical melting point for this polymer, the Vicat softening point beingnormally 5 C. C. lower than the optical melting point for a givenpolymer. Furthermore filaments spun from this polymer exhibit improvedproperties compared with those obtainable from the polymer during thelower softening point, and which are, in some respects at least, betterthan these of 66 nylon obtained under comparable conditions of spinningand drawing. Thus filaments of 6.8 nylon having tenacities of 10-12gms./denier and initial moduli in excess of 40 are readily obtained bydrawing the filaments in a heated condition. The present 6.8 nylonpolymer has other advantages compared with 66 nylon, thus higherrelative vis- 'ice cosities (R.V.) (desirable for obtaining hightenacity yarns) can easily be obtained, the equilibrium R.V. for 6.8nylon under steam at atmospheric pressure and a temperature of 280 C.being 75, compared with 50 for 66 nylon, and the filaments obtainedtherefrom have better thermal stability-comparable with those ofpolyepsilon caprolactam (6 nylon).

Accordingly therefore the present invention provides a polyamide namelypolyhexamethylene suberamide having a Vicat softening point of at least234 C. formed by polycondensation of hexamethylene diamine with subericacid. Preferably the suberic acid is obtained synthetically by thedimerisation of butadiene into cyclooctadiene and oxidation to the acid,and the polymer should normally have a relative viscosity of not lessthan 30 in order to be fibre-forming.

The invention also includes a process for the manufacture ofpolyhexamethylene suberamide having a Vicat softening point of at least234 C. wherein hexamethylene diamine and suberic acid, obtained by thedimerisation of butadiene into cyclooctadiene and oxidation to the acid,are condensed together in the presence of an acid or base stabiliserunder known polyamide forming condtions such as are describedhereinafter.

The invention further includes textile filaments spun from theabove-mentioned polymer which filaments preferably should have a modulusmeasured at 5% extension of at least 30 more preferably at least 40, atenacity of at least 7 g./denier and an extension to break of less than30%.

The invention still further includes a process for the manufacture oftextile filaments from the aforementioned polyhexamethylene suberamideby melt spinning.

The invention still further includes tyre cord yarns formed from theaforementioned textile filaments, which cords preferably have an E valuenot greater than 6.0 after processing.

The various parameters employed in defining the prod ucts of the presentinvention are determined by the methods described below.

TENACITY This is determined as for nylon 6.6 yarns on an Instron tensiletesting machine and it represents the breaking load in gms./initialdenier of the yarn under standard conditions of temperatures andhumidity (65% RH. and 68 F.) and at a rate of extension of per minute.The main result on 5 samples of 50 cms. length is taken.

INITIAL MODULUS This is a measure of the force required to effect asmall extension of a yarn of unit denier. The values quoted are of theslope, at 1% extension, of the curve obtained when the load ingms./denier is plotted against the percentage extension under theabove-mentioned standard conditions of temperature and humidity, butcontinuously on an Instron tensile testing machine at 10% extension perminute. The main result of 5 samples of 10 cms. length is taken.

MODULUS AT 5% EXTENSION This is used as an alternative to initialmodulus Where the initial modulus cannot conveniently be determined andis the average value of the slope of the above-mentioned curve between 0and 5% extension. The initial modulus and modulus at 5% extension differvery little in magnitude one from another.

EXTENSION TO BREAK This is quoted as a percentage and is measured on anInstron tensile testing machine under the same conditions as for thetenacity.

3 RELATIVE VISCOSITY This is the ratio of the viscosity of an 8.4% byweight solution of the polymer in 90% aqueous formic acid at C. to theviscosity of a 90% by weight aqueous solution of formic acid at 25 C.

INHERENT VISCOSITY This is defined as twice the natural logarithm of theratio of the viscosity of a /2% (weight of polyamide in gms. by volumeof solution in cc.) solution of the polyamide in a 90% by weight aqueoussolution of phenol under the above-mentioned standard conditions oftemperature and humidity to the viscosity of a 90% by weight aqueoussolution of phenol under those standard conditions of temperature andhumidity.

VICAT SOFTENING TEMPERATURE This is determined by a penetrometeressentially the same as the apparatus described by Edgar and Ellery atpage 2638 of the Journal of Chemical Society, 1952. The verticaldisplacement with temperature of a weighted rod resting on a block ofthe polymer is recorded. The temperature at which movement of the rodbegins is in the beginning of the softening range and the temperature atthe steepest part of the curve (generally asymotic to the temperatureaxis) is taken as the Vicat softening point. A weighted rod of -inchdiameter and total weight 300 gms. is used. The temperature is increasedat a rate of 10 C. per minute.

The suberic acid manufactured by the dimerisation of butadiene intocyclooctadiene and oxidation to the acid and used in the experimentsdetailed herein had a parity of not less than 99.5%, recrystallisationfrom water improved the purity to not less than 99.9%.

Nylon 6.8 polymer was prepared by first forming hexamethylene diammoniumsuberate salt by the addition of equimolar proportions of suberic acidand hexamethylene diamine to a suitable solvent, such a methanol or morepreferably 3:1 isopropanol/water, and crystalling from the solvent. Thesalt, containing a slight excess of diamine, was then polymerised in anautoclave under standard conditions for the preparation of 6.6 nylonpolymer. A typical autoclave procedure for the polymerisation of nylon6.8 salt is as follows:

Cycle 1.Preheat the aqueous salt solution containing, say, 60% by weightof salt to 210 C. and a pressure in the autoclave above the solution of250 psi.

Cycle 2.Heat for one hour at an internal pressure of 250 p.s.i. duringwhich time steam is bled off and the temperature rises from 210 C. toabout 217 C.

Cycle 3.Heat for a further period of one hour with gradual reduction ofpressure to atmospheric pressure, with further bleed off of steam thetemperature increasing to 265 C.

Cycle 4.Heat for a final period of from minutes to 1 /2 hours atatmospheric pressure, the temperature increasing to 280 C. Desirably,the solution in the autoclave is stirred continuously duringpolymerisation using, for example, a helical stirrer.

The temperature of the condensation reaction may be within the range ofabout 210 to 300 C. The atmosphere above the polymer may be steam, whenthe polymer can attain equilibrium, or it may be flushed continuouslywith nitrogen to enable high R.V. polymers to be obtained.

The molten polymer that results can be extruded from the autoclave evenwhen it has a relative viscosity as high as 75-110.

As an alternative to autoclave methods of preparation, nylon 6.8 saltsmay be polymerised in solution by a continuous polymerisation methodinvolving passing the salt solution through a heated narrow tube or coilas described in British Pat. Specification No. 924,630. The aqueous saltsolution used for polymerisation may suitably contain by weight of saltand 0.9% by weight of excess 4 hexamethylene diamine and the temperatureof polymerisation may be 290 C.

Molecular weight stabilisation can be achieved by the same agents as areused for nylon 6.6 polymer, acetic acid at a concentration of up to 1.0mole percent being preferred. It has been found that the equilibriumvalue for the relative viscosity of nylon 6.8 polymer is considerablyhigher at a given mole percent content of stabiliser than it is fornylon 6.6 polymer. High relative viscosity nylon 66 polymers areobtainable only by special techniques such as solid phase polymerisationof autoclave-prepared polymer, where equilibrium is displaced towardsfurther polymerisation. That very high relative viscosity nylon 6.8polymers would be easily preparable by autoclave methods was itselfunexpected, but the fact that they could be extruded from the autoclave,for example, under nitrogen pressure, for ribbon formation andsubsequent breaking up into chips was very surprising in view of thediificulty with which nylon 6.6 polymers of relatively high viscositycan be extruded from an autoclave.

In general the nylon 6.8 polymer of this invention can be melt spun anddrawn into textile filaments under similar conditions to those used inthe preparation of 66 nylon filaments. The properties of 6.8 nylon yarnare much the same as those of 66 nylon yarn with the important exceptionthat under given conditions nylon 6.8 exhibits a higher tenacity andmodulus. Thus a nylon 6.8 yarn having a given amine end group content(A.E G.) has essentially the same dyeing characteristics towards aciddyestuffs as a 66 nylon yarn of the same A.E.G. The boiling watershrinkage of nylon 6.8 yarns is generally within the range from 7-11%,i.e. similar to 6.6 nylon.

Nylon 6.8 yarns can also be hot drawn, e.g. by bemg passed over a hotplate at 120-180 C. which is positioned between the draw rolls and thesnubbing pin of a conventional drawing apparatus, to yield high tenacitylow extensibility yarns for tyre cords and similar applications.

The following examples illustrate but do not limit the invention. Inthese examples the suberic acid was, unless otherwise stated,manufactured by the dimerisation of butadiene into cyclooctadiene andsubsequently oxidised to the acid.

EXAMPLE 1 Nylon 6.8 salt was prepared as follows.

Hexamethylene diamine (154.6 lbs. of a 60% by we ght aqueous solution),isopropanol (205 lbs.), and delonised water (88 lbs.) were charged intoa suitable vessel and recrystallised suberic acid (139.2 lbs.) was addedslowly with continuous stirring. Air was excluded from the vesselinterior by a continuous flow of nitrogen gas. The internal temperaturerose during acid addition to 45 C. approximately, and after all the acidhad been added the temperature was raised to C., at which temperaturethe acid had fully dissolved, and the solution had a volume of 56imperial gallons. By very small additions of acid or amine at 70-75 C. acondition was obtained when a sample of the solution, diluted with 3times its weight of deionised Water, gave a pH reading with a glasselectrode pH meter of 7.2-7.5.

Hyflo Supercel (3 lbs.) (a registered trademark associated with a brandof diatomaceous earth) was then added to the solution, the temperatureof the solution was raised to C. and maintained at the temperature for aperiod of 20-30 minutes and thereafter the solution was filtered using asteam-heated pressure filter dressed with washed twill and printerscloth bags. 80 lbs. of a 1:3 w./w. mixture of water and isopropanol wasused to wash both the reaction vessel interior and the filter. Nyon 6.8salt could be crystallised from the solution, with incorporatedwashings, at 55-60 C.

Clean isopropanol (192 lbs.) was added to the filtered solution and thetemperature of the solution was raised to boiling. The solution whichwas then clear and bright,

was cooled slowly under nitrogen to a temperature of -20 C., at whichtemperature crystallisation of nylon 6,8 salt was complete.Crystallisation of salt began at 7075 C.

The crystallised nylon 6.8 salt was left in contact with its supernatantliquor for 2 hours before filtering oil in a nitrogen atmosphere using anutsche dressed with calico bags. The filtered salt was washed withisopropanol (3 X 80 lbs.) and dried during the course of 24-28 hours at70-75 C.

The yield of salt was 82.6% and the analyses of three separatelyprepared batches of salt are set out below.

Crude suberic acid of greater than 99.5% purity was first slurried withacetone to remove much of its colouring matter and then dissolved indemineralised water kg. of crude acid/ 140 litres of water). The acidsolution was heated under reflux for a period of /2 hour in the presenceof a quantity of carbon and Hiflo Supercel (a registered trademarkassociated with a brand of diatomaceous earth). The salt solution wasfiltered and cooled to 20 C. to efiect crystallisation of the subericacid. The crystallised acid was separated from the mother liquor byfiltration and was dried at 50 C. for 48 hours to constant weight in anair oven. The solid acid was white, had a Phosphorus (P) (p.p.m.); Iron(Fe) (p.p.n1.)

The salt was polymerised using an autoclave and a charge of a 60% byweight solution of the salt in water. The procedure followed was thefour-cycle procedure described in detail hereinbefore and the autoclavecharge was stirred continuously throughout polymerisation using ahelical stirrer. In the final stage of the four-cycle process thepolymer was heated for 1 hour under steam at atmospheric pressure. Aspolymer antioxidant, 40 p.p.m. of copper as copper acetate and 1,000p.p.m. of iodine as hexamethylene diammonium iodide were incorporated inthe charge to the autoclave (the parts being by weight and based on thepolymer) and molecular weight stabilisation was achieved using 0.25 molepercent based on the salt of acetic acid.

The finished polymer was extruded from the autoclave in the form of aribbon, cooled and cut into chips. The polymer chip had a Vicatsoftening point of 234 C. and a relative viscosity of 51.2.

The polymer as prepared above was melt spun through a 34-hole spinneretof a screw extruder at a spun-yarn Wind-up speed of 669 ft./ minute togive a spun denier of 1140. The melt in the screw extruder wasmaintained at a temperature of about 290 C. The yarn was cooled belowthe spinneret by blowing air onto the extruded filaments and the yarnwas then passed through a steam conditioner. A spinning finish wasapplied to the yarn to give an oil on yarn content of 0.4% by weight.The yarn had a relative viscosity of 57.4.

The as-spun yarn was hot-drawn by means including a 4-6-inch lengthheater plate maintained at 180 C. immediately after spinning at a drawratio of 5.9 and a windup speed of 750 ft./ minute to give yarn with thefollowing properties:

Tenacity-l2.l g./d., Extension to break-18%, and Modulus at 5%extension-40 g./d./ 100% extension EXAMPLES 2-7 A number of batches ofnylon 6.8 polymer were made according to the following procedure.

(All less than 5) 2 2 melting point of 141-1425 C., and a solution ofthe acid in 10% sodium hydroxide was almost colourless. The yield ofacid was 94%.

Hexamethylene diamine (re-distilled) was dissolved in pure methanol toform a solution containing about 4 kg. of diamine per litres ofmethanol. Suberic acid was added in such quantity that the diamine waspresent in 4 mole percent excess and the mixture was heated under refluxwith stirring until all the acid had dissolved. The solution was cooledto below 25 C. with continuous stirring to effect precipitation of thenylon 6.8 salt, the salt was filtered off, washed with cold methanol anddried at 60 C. under a pressure of mm. Hg.

The yield of salt was 52% based on the weight of suberic acid used andon analysis the salt was found to contain an amine end group content(A.E.G.) of 6915/ 10 gms. and a carboxyl end group (C.E.G.) of 6913/ 10gms. (Theory demands 6897 end groups (A.E.G. or C.E.G.) per 10 gms.)

For the purpose of molecular weight stabilisation about 0.25 molepercent of acetic acid stabiliser was incorporated with the salt and thepolymerisation was carried out in all cases under closely similarconditions of temperature, pressure and duration of reaction, and thepattern of reaction was very similar to that described under Example l.

The polymer obtained were rod-spun at a temperature of 270285 C. usingrod spinning equipment and at a wind-up speed of 400 ft./minute.

The spun yarns were drawn at a delivery speed of 50 ft./minute both overa cold surface plate at room tem perature and over a 4-6-inch lengthheater plate maintained at C. The boiling-water shrinkage of the yarnswas also investigated.

The results obtained are set out in Tables 1 and 2.

These results demonstrate that nylon 6.8 polymers can be made that arecapable of yielding yarns of outstanding potential for use in many ofthe present day outlets for textile fibres.

TABLE 1.SALT, POLYMER AND SPUN YARN PROPERTIES OF NYLON 6.8

Yield Vicat of Salt analysis Polymer analysis Softening Spinning Wind-upAnalysis or yarn salt, point, temp. in No. of speed, n

percent A.E.G. C.E.G. I.V. .A..E.G. C.E.G. 0. C. filaments ft,./min. I V11.13 G C.E.G

67 6, 865 6, 947 0. 819 33 91 235 270 5 400 0. 006 30. 4 78 7o 6, 914 6,894 0. 914 as. 5 72 236 270 5 400 0. s92 34. 4 (so 7 7. 5 6, 919 6, 8740. 88 40. 6 80 235 270 5 400 0. 866 33. 3 80 66 6, 914 6, 874 0. 911 42.8 77 235 270 5 400 0. 942 35. 4 73 as a, 913 6,845 0. 916 40. 9 so 235270 5 400 0. 915 as. o 68 TABLE 2.DRA'WING CONDITIONS AND DRAWN YARNPROPERTIES OF NYLON 6.8

Properties of yarn I.M. at Boiling I.M. at 1% ext. water 1% ext. DrawIIot plate Tenacity, Extension, g./d./100% shrinkage, Tenacity,Extension, g./d./l% ratio temp. in C. Denier g./d. Percent ext. percentDenier g./d percent ext.

Exam le:

2.3 5.0 Room temp.-- 24. 9 7. 54 24. 4 38. 11. 95 26.1 6. 85 37.0 29. 63 5.0 .do 24.0 7. 92 24. 3 40.1 11.6 28. 5 6. 20 37. 3 25. 3 6. 0 18019. 8 11. 15 14. 0 53. 2 9. 83 25. 8 8. 51 23. 5 32. 5

4 5.0 Room temp... 25. 1 7. (i5 23. 7 39. 5 11.5 31. f) 5. 00 35. 3 26.7 6. 0 180 20. 0 l1. 6 15. 7 52. 0 9. 3 26. 0 8. 8'.) 24. 4 32. 4

5 4. 75 Room temp... 26. 6 6. 68 23. 1 37.0 11.5 32. 8 5. 53 37. 7 25, 66. 0 20. 4 11- 4 14- 4 54. 4 9. 53 26. 8 9. 07 23. 4 35. 0

6 75 Room p--- 3 6 79 26.1 38.6 11. 4 216 95 33' 6 m 9 5. 75 180 21.010- 5 l4- 8 52. 95 9. 33 23.9 9. 0 23. 9 35. 3

7 5. 0 Room temp.-- 20.0 6. 8!) 23. 1

EXAMPLE 8 EXAMPLE 9 Amine end group content (A.E.G.)- 49.1 per 10 gins.

For the purpose of comparison only a sample of suberic acid obtained bythe oxidation of castor oil was purified by conversion into the ethylester which was fractionally distilled, (the material boiling at 138 C.to 141 C. t 0.7 mm. Hg pressure being collected), and then hydrolysedback to the free acid. 6.8 nylon salt was prepared and polymerised bythe process described with reference to Examples 2-7. The resultantpolymer had Vicat softening point of 228 C. and an inherent viscosity of0.79 and was rod spun to yield a 30 denier 10 filament (30/10) drawnyarn. Conditions of spinning and drawing and yarn proper-ties are givenin Table 3.

TABLE 3.SPINNING AND DRAWING CONDITIONS AND YARN PROPER- TIES OF NYLON6.8 OBTAINED USING SUBERIC ACID MANUFACTURED BY THE OXIDATION OF CASTOROIL Spinning and drawing conditions Yarn properties Spinning SpinningDraw Drawing Drawing Ext. at I.M. g./d./ speed, temp, ratio, speed,temp., Tenacity, break, 100 ext. ft./min. C. max. it./niin. C. g./d.percent at 1% ext.

Carboxyl end group content (C.E.G.)74 per 10 gms. Relativeviscosity42.9. Vicat softening point-235 C.

These results indicate that polymer prepared using suberic acid obtainedvia the oxidation of castor oil, even after an uneconomically attractivepurification process, yields a polymer of lower melting point and a yarnof inferior properties compared with those obtained starting fromsuberic acid obtained by the synthetic route referred to herein.

EXAMPLE 10 Nylon 6.8 polymer prepared by the process described inExample 1 containing 0.3% Ti O and having a Vicat softening point of 234C. and an R.V. in the range 35-40 was spun and drawn into a 30/10 yarnusing a standard gravity melter for spinning. The spinning and drawingconditions and drawn yarn properties are given in Table 4.

TABLE 4.SPINNING AND DRAWING CONDITIONS AND YARN PROPERTIES OF 30/10 6.8NYLON YARN CONTAINING 0.3% Ti102 Spinning and drawing conditions Yarnproperties Modulus 9% Spinning Drawing Extension extension speed, Temp,Spun Draw 'Iemp., Speed, Tenacity, at break, at 5% it./min. C. denierratio (3. it./min. g./d percent extension 3, 930 285 2. 62 Room-. 1, 5206. 0 26. 9 30. 8

prepared in a continuous polymerisation unit of the kind described inthe aforementioned British patent specification.

The above yarn was warp-knitted into a shirting fabric which was heatset at C. for 27 seconds without discolouration (in contrast to 66 nylonwhich has to be set at about 220 C. for 28 seconds and discolours). Thefabric had b chromaticity value of 0.333 before bleaching that is thesame as for 6 nylon, the 66 nylon giving a value of about 0.320; bchromaticity is a measure of the yellowness of a fabric and is definedas:

. brefiectance b chromatlclty z r+g+b refiectanees where r, g, and b arethe red, green, and blue reflectances as measured using a trichromaticcolourimeter.

EXAMPLE 1 1 The polymer of Example 10 was spun and drawn into 70/20 and70/34 in the manner described in that example. Spinning and drawingconditions and drawn yarn properties are given in Table 5.

TABLE 7.-PHYSIGAL PROPERTIES OF 840/140 6.8 NYLON TYRE CORD YARN Ext. atI.M. at 5% Tenacity, break, extension,

Yarn sample Yarn R.V. g./ percent g./d./100% ext.

025 62. 9 9. 9 12. 6 52 C26 62. 9 9. 5 13. 2 58 66 nylon tyre cord 50 9.16.0 40. 45

The figures for 66 nylon, quoted for comparison, were determined on atypical sample of commercial tyre cord yarn.

Unprocessed tyre cords were prepared in a 2/840 12S/12Z construction.These cords were processed by TABLE 5 Spinning and drawing conditionsYarn properties Spinning Drawing Ect. at speed, Ternp., Spun Draw Temp.,speed, Tenacity, break, ftJmin. denier ratio C. ftJmin. g. percent Yarntype:

70/20 2, 965 285 240 3. 3 Room 1, 520 5. 1 28. 9 70/30 3,930 285 170 2.5do 1,520 5.5 32.9

The above yarns were false-twist crimped over a range of temperatures.The bulk developed by the yarn was determined by measuring the crimpratio. The results of these experiments are quoted in Table 6. Resultsobtained for 66 nylon are included for the purpose of comparison.

TABLE 8.PHYSICAL PROPERTIES OF 2/840, l2S/12Z 6.8 NYLON TYRE CORDSUnprocessed cords Processed cords Strength Ext. at loss per Breakingbreak, E10, Breaking Ext. at E10, 100,000 load lbs. percent percent loadbreak percent flexes, lbs.

Yarn sample:

C 33. 1 20. 0 9. 8 31. 6 11. 7 4. 9 2. 1 2 33. 1 22. 7 10. 2 34. 0 14. 05. 5 2. 1 66 nylon tyre cord 30.0 20-24 10 30. 0 16 7. 5 2. 5

where Lizlength of yarn (crimped) When under a load of 0.001 g./denierwhen suspended freely.

Lzzlength of yarn (decrimped) when under a load of 0.1 g. denier whensuspended freely.

The figures for crimp ratio obtained for 6.8 nylon are notably betterthan those obtained for 6.6 nylon.

EXAMPLE 12 6.8 nylon polymer having an RN. of 62.9 and obtained in themanner described in Example 1, was spun at 758 The parameter Erepresents the percentage extension of the cord when subjected to a loadof 10 lbs.

The above results indicate that tyre cords of 6.8 nylon have superiorproperties to those of 6.6 nylon.

What is claimed is:

1. In a process for the manufacture of high molecular weight,fiber-forming polyhexamethylene suberamide by the condensation ofhexamethylene diamine with suberic acid at about 210-300 C., theimprovement which comprises using in said condensation suberic acidprepared by the steps of dimerizing butadiene to form cyclooctadiene andthen oxidizing the cyclooctadiene to form the suberic acid.

2. The process of claim 1 wherein said suberic acid is purified prior tocondensation and wherein a salt of approximately equimolar proportionsof said suberic acid and hexamethylene diamine is formed by heating an 0aqueous solution of said acid and diamine and said salt is polymerizedat superatrnospheric pressure and elevated temperature in the presenceof a slight excess of hexamethylene diamine to produce apolyhexamethylene suberamide having a vicat softening point of at least234 C. and a relative viscosity of at least 30 as measured using an 8.4weight percent solution of the polymer in 90% aqueous formic acid at 25C.

References Cited UNITED STATES PATENTS Spanagel 260-78 Flory 260-78Carothers .260-78 Bell et a1. .i 260-78 Monroe 260-78 0 1 2' OTHERREFERENCES Journal of Polymer Science, vol. 28, 1958, pp. 443 445,Trifan et al.

Polyamide Fibers, second edition, 1966, p. 125, Floyd.

HAROLD D. ANDERSON, Primary Examiner U.S. Cl. X.R.

